The study aims to determine the prevalence of drug resistance mutation (DRM) in virally suppressed HIV infection, and the impacts of regimen change and the presence of low level viremia. Adults living with HIV infection on antiretroviral therapy (ART) with full viral suppression would be recruited. Cases are patients planning for regimen switch, while controls are those with and without low level viraemia (LLV) not planned for switch. Blood samples would be collected before and after switch. Sequencing would be performed to identify DRM present in HIV-1 proviral DNA.